I. Field of the Invention
The present invention relates to footwear made of synthetic resin materials. More particularly, the present invention relates to a system and method that is used to make multi-color footwear by combining resins of different color to produce a pattern of different colors in the footwear.
II. Description of the Related Art
Footwear made from light-weight materials such as closed cell resin have gained popularity in recent years. One of the methods to manufacture such footwear is molding where resin is injected into a mold. The resin solidifies and assumes the permanent shape of a footwear. the temperature decreases in the mold. U.S. Reissue Patent Re. 29,265 and U.S. Pat. No. 3,962,387 both issued to Hendry and incorporated by reference herein describe a closed cell foam plastic molding machine for molding articles made of closed cell foam plastic. The Hendry patents describe extrusion equipment for injection molding of granular thermoplastic materials to make foam products. The foam is provided by mixing an inert gas, such as nitrogen, into molten thermoplastic material. Multiple molds may be used with a given injection machine to facilitate rapid processing with extended cooling times for the individual molds.
U.S. Pat. No. 6,439,536 issued to Piccolo is incorporated herein by reference and describes the special problem of molding shoes with expanding plastic materials. A two piece undercut mold with a one piece core define a mold cavity that is fed through filing channels. Expanding plastics, and particularly ethylene vinyl acetate (EVA), may expand from 20% to 80% by volume upon the opening of such molds, where it is desirable to open the molds quickly to avoid product deformation. Alternative plastics for use in these applications at least include polyurethane and PVC. Lateral through-holes may be formed in the shoe upper by the use of side inserts. The base section and the strap of a sectional footwear may be molded separately. The base section made by injection molding may expand in size when removed from the mold, but it usually shrinks as it cools down. U.S. Patent Application Publication # U.S. 2004/0231190 describes a particular coefficient of expansion that is generally desirable when molding EVA shoes. It also discloses a molding process in which the base section and the strap of the footwear are separately molded and then assembled together.
Prior to the present invention, shoes made by injection molding usually contain one primary color throughout the entire footwear. This simple color scheme may be due to the relative simplicity of plasticizing and injecting raw materials of a single color. However, footwear with multiple colors dispersed throughout the base section may be desirable because they are stylistically more attractive. Moreover, it may be productively advantageous to utilize raw materials of different colors. This advantage becomes more apparent when there is a shortage of raw material of a particular color.
No methodology has been disclosed for molding a shoe that contains two or more colors being dispersed throughout the entire footwear. There is therefore a need for a system and a method for making such multi-color footwear. All references cited in this disclosure are hereby incorporated by reference.